With reference to FIG. 1, a fuel grade ethanol production process 100 typically includes the steps of milling, saccharification, fermentation, distillation and evaporation (see for example U.S. Pat. No. 7,572,353 to Griend). As shown in FIG. 1, the typical process generally begins by milling grains and combining the milled grains with water and enzymes to break down the grains to produce sugars (saccharification). The mixture is then typically combined with yeast and allowed to ferment.
In the fermentation portion of a typical process, a slurry of milled corn is fermented to produce a beer having a concentration of ethanol that is generally less than 15% by volume. In the distillation portion of a typical process, the ethanol in the beer is extracted in distillation columns. Distillation columns typically have a multitude of horizontal trays for bringing rising ethanol vapor and descending liquid into contact. In a distillation column, low pressure steam percolates up through the beer as the beer cascades from higher trays to lower trays. As the rising steam heats the beer, the ethanol in the beer evaporates and rises to the top of the column where it exits as a vapor. The remaining water and other grain material in the beer descends to the bottom of the column to exit as “beer bottoms” or “whole stillage.” This whole stillage material is typically then separated via whole stillage centrifuges into solids and what is known as “thin stillage.” The resulting solids, known typically as Wet Distiller's Grains with Solubles (WDGS) are then typically dried to produce Distiller Dried Grains (DDG) which is a valuable feed ingredient. The thin stillage is then typically reduced via an evaporation process where liquid is boiled away from the thin stillage to produce a syrup which can also be dried in the DDG dryer to further increase the output of the animal feed co-product.
While tried and true, the present methods for producing ethanol leave important oils, biomass and other important by products (such as glycerol) unprocessed. Accordingly, the present invention provides a more efficient process for producing ethanol which includes stillage fermentation.